<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>JavaScript</title>
    <script type="text/javascript" >
    alert(123);
    </script>
    <script type="text/javascript" src="./js.js"></script>
</head>

<body>
    <h1 id="h1">JavaScript</h1>
    <h1>123</h1>
</body>

</html>